In all cellular communications networks, there are opposing requirements for high spectrum efficiency and high area availability, or coverage. As a Fourth Generation (4G) technology, Long Term Evolution (LTE) is expected to provide high spectrum efficiency. Namely, LTE is expected to provide three to four times higher spectrum efficiency than High-Speed Downlink Packet Access (HSDPA) Release 6 for the downlink, and two to three times higher spectrum efficiency than High-Speed Uplink Packet Access (HSUPA) Release 6 for the uplink. In addition, as with any cellular communications network, LTE must provide 90%-95% coverage, which is referred to as Carrier Grade of Service (CGOS) for coverage. The requirements for high spectrum efficiency and coverage are opposing in that a small frequency reuse factor (N) is desired in order to achieve high spectrum efficiency but, in general, a high frequency reuse factor (N) is desired in order to decrease out-of-cell interference and therefore increase coverage. A maximum spectrum efficiency is achieved when the frequency reuse factor (N) is 1 such that the entire spectrum is reused in each cell of the cellular communications network. However, when the frequency reuse factor (N) is 1, out-of-cell interference is at its maximum and, therefore, coverage is at its worst.
Spectrum efficiency can be roughly determined by a minimum Signal-to-Interference-plus-Noise (SINR) needed for a wireless communication link, or airlink, to survive in the cellular communications network. For example, an Advanced Mobile Phone System (AMPS) typically requires a SINR of greater than or equal to +18 decibels (dB). Thus, in order to achieve the CGoS in AMPS, a very large frequency reuse factor of N=21 is needed in order to achieve the needed SINR. As another example, Code Division Multiple Access (CDMA) system can operate with SINR values as low as −14 dB as a result of the processing gain due to the spreading and dispreading process. As such, a frequency reuse factor of N=1 can be used in the CDMA system.
For LTE, a minimum SINR needed to maintain a wireless communication link is approximately −5 dB. However, for a fully loaded LTE network having a frequency reuse factor of N=1, test results show that the SINR at cell edges can be lower than −12 dB. Therefore, there is a need for a system and method for improving coverage in an LTE cellular communications network while maintaining high frequency reuse.